Was thinking more about this.. I haven't done a lot of these and mostly years ago. Back then I probably did more as you said - cork/high tack. Not a dozen times, but I did re-use them. Today's cork gaskets may hold up better also. I do prefer the rubber, but they may be less forgiving if the cover is not flat. I will agree if rubber does not seal by itself, my experience is that RTV sometimes seams to make it worse